Herpes simplex viruses (HSVs) cause a variety of human diseases and the nervous system plays a central role in its pathogenesis. HSV1 and HSV2 establish lifelong latent infections within sensory peripheral ganglia. In addition, the nervous system is the major target of morbidity and mortality resulting from herpetic encephalitis and neonatal herpes. Our overall goal is to understand the mechanism by which the virion glycoproteins mediate virus entry into cells. After the initial interaction between virion gC and host cell heparan sulfate, four glycoproteins, gB, gD and the gH/gL complex, mediate virus-cell fusion at the plasma membrane. gD functions by binding to a cellular receptor to trigger fusion events involving gB and gH/gL. Four receptors have been identified. One, called HveA, is a member of the tumor necrosis factor receptor family. We propose three specific aims: 1) to further characterize the interaction between HSV gD and its receptor HveA; 2) to study structural and functional properties of HSV gH/gL and gB; and 3) to examine the consequences of gD-receptor interactions for virus entry. We solved the 3-D structure of gD bound to HveA. The gD/HveA interface involves portions of the first two cysteine rich domains of HveA and a hairpin structure at the N-terminus of gD. In Aim 1, we will study the properties of a set of mutants with alterations in each of the contact residues of HveA and gD. We will investigate the significance of a conformational change in gD when it binds HveA. In Aim 2, we will begin crystallization trials on gB and gH/gL. Concurrently, we will solve the disulfide bond arrangement of gH and gL and study the properties of gD/gH chimeras. We will examine the significance of conformational changes in these proteins brought about by changes in pH or temperature. In Aim 3, we will study the entry process using: 1) chemical cross-linking of virus and cell molecules; 2) direct examination by IFA; 3) cell-cell fusion as a model of entry; 4) FACS to follow structural changes in receptor and viral glycoproteins during entry. These studies will provide a better understanding of HSV entry and enable the design of strategies for combating HSV infection and pathogenesis by targeting elements of the entry machinery.